A building as big as an aeroplane hangar, but not so high. It 's painted all over with brown and yellow stripes. It stands on the edge of the water in as neat a little cove as you ever see.'

'What 's in this shed?'

I dunno, sir. It was dark when I was there. I lay down in the dunes near by, reckoning to have a closer look when it got light, in case there was a dinghy in it. I was trying to find a way in when I see you coming, so I ran down on to the beach so as you'd spot me.'

'Did you find anything else on this bit of no-man's-land ?'

'No, sir, that 's the lot.'

Algy thought quickly. The absence of the motor-boat was now explained, but he was more concerned about the shed Briny had described. That it was a secret supply depot seemed certain, and this, no doubt, accounted for the notice-board forbidding people to land. But Briny's description of the shed had been vague, and he felt that while he was there he ought to obtain more detailed information, for the Admiralty would be anxious to have full particulars. 'How far away is this shed ?' he asked.

About a mile, sir, I reckon.'

And as far as you know there was no guard over it ?'

I didn't see a soul, sir.'

In that case we'll go along and have a look at it. Get in.'

Briny started, 'Get in what, sir ?'

'This aeroplane-what else do you think I mean ? You can't see any motor-cars about, can you ?' 'What, me, sir ?'

'Yes, you. Don't argue.'

'You don't mean you're going to fly there, sir ?'

Algy wasted no more words. He bundled Briny into the back seat, and then, climbing in himself, taxied swiftly along the beach.

'Steady on, sir, me 'at 's blowing off,' roared Briny, who was clutching at the sides of the c.o.c.kpit.

Algy did not take off, for the short distance he had to travel made it unnecessary, and five minutes brought them to within sight of the building. He saw at once that Briny's description of it, as far as it went, was correct. The shed was a large but low structure, covering nearly half an acre of ground, built in a dip in the dunes at the landward extremity of a tiny cove so regular in shape that there was reason to suppose that it was artificial. The building stood at the very edge of the water; indeed, it was obvious that at high tide a boat of shallow draft would be able to moor up against the huge sliding doors; yet so cleverly camouflaged was it, in the same drab colours as the surrounding sand, that it would have been possible to fly over it at a low alt.i.tude without suspecting that it was there. It appeared to be absolutely deserted.

Seeing that it was impossible to taxi right up to the shed on the landward side on account of the dunes, Algy took the machine on to the water, and after raising his landing-wheels, made a cautious approach, prepared to take off the instant anyone appeared; but by this time he felt confident that had a guard been on duty he must have heard the approaching aircraft and revealed himself.

Nevertheless, he did not relax his caution as he taxied on, very slowly, until the Didgeree -du was alongside a wooden landing-stage that now appeared near the doors.

'Go and have a look round to make sure that n.o.body's about,' he told Briny. 'I'll stay here in case of accidents. If it's all clear I'll join you.'

Briny was soon back. 'Can't see a thing, sir,' he reported.

'What 's in the shed ?'

I can't see, sir. There ain't no winders.'

'That's queer. You'd have thought there'd have been some sort of lighting.' Algy got out and tried the doors, but, as he expected, they were locked.

Meanwhile, Briny had climbed to the top of a dune, high enough to overlook the roof. '

There's skylights on top,' he announced.

'Skylights usually are on top, Briny,' smiled Algy. 'I'd better have a look. Give me a bunk up.'

Algy was soon on the roof which, like the rest of the building, was built of corrugated iron. Crawling to the skylight, he peered down through it. For a few seconds he could see nothing, for owing to the inadequate lighting the interior of the shed was in dim twilight.

Presently, however, he was able to make out the broad details, enough to tell him that the shed was, in fact, a naval depot -for submarines, chiefly, he thought, judging by the torpedoes and a formidable stack of oil drums. Having seen enough for his immediate purpose he slid off the roof.

It seems to be an ideal spot to plant a bomb,' he declared as they went back to the machine. And the sooner the better,' he added. 'If we can get rid of this lot, submarines coming here, relying on finding fuel, might find themselves stranded. I should say the sub. we sank was making for this place. Come on, let's get back; the C.O. ought to know about it.'

More than a little satisfied with the result of his survey, Algy turned the nose of the Didgeree-du to the mouth of the cove, and opening his throttle, roared away in the direction of the base.

So concerned was he with getting back that beyond keeping a watchful eye on the horizon for shipping he paid little attention to the sea below; so when Briny tapped him on the shoulder and pointed downwards, he followed the outstretched finger with a twinge of anxiety-anxiety that grew rapidly to acute alarm when his eyes found the object that Briny had spotted. Unquestionably, it was the wreckage of an aeroplane.

Cutting his engine, he side-slipped steeply towards it, and at a thousand feet his worst fears were realized, for showing just above the gently lapping waves was the circular red, white, and blue nationality mark of a British aircraft. For a moment he experienced a feeling of relief as he remembered that the Dingo had been lost, for he a.s.sumed, not unnaturally, that this must be the remains of it; but then he recalled that Ginger's machine had been burnt out, whereas there was no sign of fire on the wreckage.

As quickly as he dared he put the Didgeree-du down on the water and taxied up to the wreck. One glance was enough to tell him the worst. The machine was one of their own ; and if further proof were needed, the boomerang device on the crumpled fuselage, with the name Willie-Willie below, provided it. It was Biggles's machine. And the reason for its present condition was apparent, for through fuselage and wings were the unmistakable gashes of shrapnel.

As white as death, Algy flung off his flying-coat and slid into the water, groping blindly for the c.o.c.kpit. He found it. It was empty, as was the spare seat. Gasping, he returned to the surface, and climbed up on the nearest float of his own machine, from whence he stared at the wreckage as if he could not believe his eyes. His brain seemed paralysed.

Biggles had been shot down. That was obvious. And judging from the number of hits registered on the plane, and the mangled condition of it, the crash must have been a terrible one. He tried not to believe it, but there was no getting away from the grim evidence before him.

It was Briny who discovered that the engine was missing. 'It looks as though it was chopped *out with an 'atchet,' he declared in a sombre voice.

'Then that settles it,' returned Algy miserably. 'They shot him down and salvaged the engine for their own use. They would, of course.' He said no more. There was nothing else to say. Minutes pa.s.sed and still he stood on the float, staring dumbly at the wreck.

At last, realizing that no good purpose could be served by remaining, yet hating to leave the spot, he climbed slowly into his c.o.c.kpit. His eyes wandered over the surrounding sea.

Briny guessed what he was looking for. 'It ain't no use looking for the body,' he said gruffly. It 'ud sink. I remember 'We'll get back,' broke in Algy harshly, and taking off, he raced on full throttle for the base.

'Where 's Mr. Hebblethwaite ?' he asked the Flight-Sergeant, who came running along the catwalk to meet them.

I don't know, sir,' was the unexpected reply. 'We haven't seen him for a couple of hours or more.'

'He didn't by any chance go with the C.O. after all ?'

'No, sir. The C.O. hasn't come back yet.'

I'm afraid he-won't be coming back,' said Algy slowly. He glanced at the Platypus, the spare machine, still riding at her mooring. 'Mr. Hebblethwaite must be about somewhere.'

'That's what we thought, sir, but we can't find him.'

Briny and the Flight-Sergeant watched in embarra.s.sed silence as Algy unfastened the strap of his flying-cap and lit a cigarette. 'The war still goes on,' he said evenly. 'It can't stop because the C.O. is-missing. I am now in command here. Get my machine up to the derrick and sling a torpedo on it.'

Tut are you going off again right away, sir ?' asked the Flight-Sergeant.

I am,' answered Algy curtly. 'You'd better make a thorough search for Mr.

Hebblethwaite-he may have fallen and hurt himself. If he turns up tell him to stand by until I return. Those are my orders.'

The Flight-Sergeant saluted. 'Very good, sir.)

CHAPTER X.

GINGER GOES EXPLORING.

HAD Ginger been aware of Algy's tragic discovery his state of mind would have been more hara.s.sed than it actually was-although he would have found it difficult to believe that possible.

He had been awakened by the roar of the two machines taking off to begin the search for Briny; he had guessed what they were going to do and hastily pulled on his slacks with the intention of confirming it. Outside he was met by the Flight-Sergeant, who gave him Biggles's order that he was to stand fast until the search party returned.

Annoyed with himself for having overslept, Ginger made his way back to his quarters, finished dressing, and had his breakfast. Thereafter he wandered about for the best part of an hour, killing time by examining the stores and visiting Roy in the signals room.

Bored, he was on his way to the mess when it struck him that it was a good opportunity to explore the extremity of the cave-not so much for any particular reason as from idle curiosity. So fetching an electric torch from the stores, he started off over the loose rocks which began where the water ended. It struck him that he ought to have told the Flight-Sergeant where he was going, in case the machines returned before he did, but on second thoughts he concluded that this was unlikely, and proceeded on his way.

It is often fascinating, if futile, to speculate what might have happened if certain events had gone otherwise than they did, or to trace the tremendous consequences of incidents which, at the time, seemed of trivial importance. Thus it was with Ginger now. Had he returned and reported his proposed expedition to the Flight-Sergeant, the Flight-Sergeant would have known where he was; he in turn would have informed Algy, who, instead of taking off with a torpedo on board, would have first tried to locate him in order to tell him about his discovery of Biggles's machine. But Ginger did not return, and as he proceeded on over the rocks he would have been incredulous could he have foreseen the result of his failure to do so. It is certain that the history of 'Z' Squadron would have been altogether different from what it actually was.

He discovered, as he rather expected, that beyond the area of flat rock on which the depot was established the cave rapidly diminished in size, closing in on all sides until it was no more than a high, narrow tunnel, the floor of which was strewn with rocks worn round by centuries of erosion. He could not see why this should be, for the sea did not come as far, ending as it did in a rather slimy pool just beyond the depot. However, he a.s.sumed that exceptionally high spring tides penetrated farther into the island than they supposed, and made a mental note to warn Biggles of this, for it seemed not unlikely that at such times the floor of the depot would be inundated.

Thereafter the cave narrowed so rapidly that he was quite prepared for it to end abruptly at any moment ; so confident was he that this was the case that he almost abandoned his survey, and it was only by the merest chance that he squeezed through a gap and turned the beam of the torch on what lay beyond. To his surprise he found that the cave, while not broadening to any great extent, became very high-so high, in fact, that the light of the torch failed to reach the ceiling.

The picture that now presented itself was in the nature of a gigantic crack, or fissure, the floor of which sloped upwards. Both the floor and walls of the cavity were polished smooth in a manner that suggested that water was responsible, and again this puzzled him not a little, for he could not imagine that the tide would rise so high. Wonderingly he took a few paces forward, and a clue to the mystery was provided when, stepping on something soft and looking to see what it was, the light of the torch revealed the decomposed carca.s.s of a seagull.

On the face of it there was nothing remarkable about finding the body of a gull there, for there were legions of them on the outside of the rock, but his common sense refused to accept the obvious explanation-which was that the gull had made its way right up the cave in pitch darkness. Why should it ? He had never seen a gull in the cave, or even one that looked like entering the cave, so why should this particular bird proceed up it so far and then perish miserably ?

A few moments' reflection were sufficient to cause Ginger to reject the supposition that the gull had flown up the cave. Yet the gull was undoubtedly there. How had it got there ? There could only be one answer to that question. There was another entrance to the cave ; it was (he reasoned) through this other entrance that the water had entered, and since water does not run uphill, the other entrance must be higher than the one they habitually used. This at once presupposed that the gull had been carried to its present position by water flowing down through the rock.

Hunting about, Ginger soon found what he sought-a small pool in a depression in the floor. Dipping his fingers into it, he tasted it, and discovered that it was fresh, without any suggestion of salt. After that, deduction was fairly simple. Somewhere ahead, possibly on the top of the rock, there was a watershed through which rain water made its way down into the cave.

He went on now with renewed interest, for it seemed probable that he had found a way to the top of the rock ; and if this was so it would serve a very useful purpose in that they would be able to command a much wider view of the ocean than had been possible from the mouth of the cave. So he pressed on, anxious to ascertain if this was really so.

The floor now began to rise steeply, strengthening his conviction that the fissure went to the top of the rock. It was tiring work, for not only was he travelling uphill, but he was often compelled to put the torch in his pocket to leave both hands free while he climbed a scree of loose shale, or an awkward-shaped boulder.. However, he encountered no serious obstacle until he was brought to an abrupt halt by a face of overhanging rock some twelve feet high which completely blocked his path. Examining it closely, he suspected that he must be near the top, for a steady trickle of water flowed over the edge of the rock, which was worn to the smoothness of polished marble. It was covered with green slime, and to make matters more difficult, did not present a single foothold.

Disappointed at the thought of being thwarted just when success seemed a.s.sured, he sat down to get his breath and at the same time think out a way of overcoming the obstruction. He soon found one. There were plenty of pieces of loose rock lying about; these he proceeded to collect and pile one upon the other, forming a cairn, from the top of which he was able to reach the top of the obstruction. The rest was comparatively easy. Or so he thought.

How far he was wrong he discovered when, dragging himself up on the rock, his dangling legs struck the top of the hastily constructed cairn and sent it avalanching down the cave with a crash that brought his heart into his mouth, for until he realized what it was he had a horrible thought that the cave was collapsing on him. He perceived at once that this was going to make it very difficult for him to get down again. And it was only the first disaster, for as he was squirming over the edge of the rock, the torch, which he had put in his pocket, fell out, and went crashing down the way of the cairn.

Reviling himself for his carelessness, he dragged himself up and sat panting in utter darkness on the edge of the rock, thoroughly alarmed, wondering whether to go on or to try to get back, realizing that the descent of the rock on which he was perched was not going to be easy. Even if he got down without hurting himself, and then found that the torch was broken-as seemed highly probable-his return was going to be a slow and tedious business. He remembered with relief that he had a box of matches in his pocket, but feeling in it with nervous haste, he discovered to his intense disappointment that there were only three matches in it.

He knew that, as he had already been away from the depot much longer than he originally intended, he ought to start back and leave further exploration for a future occasion, when he could begin more suitably equipped. And he had, in fact, made up his mind to return forthwith when, happening to stare into the darkness ahead, he saw a grey streak not very far away, a patch of reflected daylight which could only mean that he was near the end of his journey.

In the circ.u.mstances it was only natural that he should begin walking towards it, feeling his way in order to conserve his precious matches. But he had only taken a few paces when he stepped into a void. Feeling himself falling, he made a terrific effort to preserve his balance ; but it was too late, and the next instant, with an abruptly terminated cry of horror, he was splashing frantically in ice-cold water.

To fall into a pool of cold water at any time is bad enough, but to do so in utter darkness, in such a place as Ginger now found himself in, was terrifying. Unable to touch bottom he had to swim, and instinctively struck out for the rock from which he had fallen, only to discover to his dismay that it was as smooth as a tombstone and the top was beyond his reach.

Had it not been for the one patch of grey light his plight would have been desperate indeed, and it was probably as much in order to escape the suffocating darkness as any other reason that he struck out towards it. To his unspeakable relief, after swimming a few strokes he found that he could touch bottom, so he staggered on through the water towards the blessed light, which, he felt, was the only thing that saved his sanity.

As he approached the spot it grew definitely lighter, and it was with a prayer of thankfulness that he finally dragged himself towards an aperture through which he could see what he had begun to wonder if he would ever see again-the blue sky. His haste to reach it was nearly his undoing, for he had forgotten all about his steep climb, and he was in the act of stepping forward when a spectacle so unexpected, and so alarming, met his eyes that a gasp of despair left his lips as he recoiled from it. The ground in front of him dropped sheer for a full four hundred feet. Indeed, it was even worse than that, for his precarious perch actually overhung the abyss, and he dropped on his knees in a spasm of vertigo as his eyes surveyed the dizzy height.

For a moment or two he remained still, fighting the weakness, angry that he should have succ.u.mbed to it. Then, taking himself in hand, he made a quick inspection of his position. He saw that instead of emerging on top of the rock as he had a.s.sumed would be the case, the fissure had ended some twenty feet below the top of the cliff, which he could now see above him. He perceived, too, that although this twenty feet of rock face was sheer, the surface was rough, and offered finger holds by which a skilled mountaineer might have made his way to the top ; but he was not a skilled mountaineer, and the mere thought of trying to make the short but terrifying journey to the top made him feel physically sick.

Lying flat, he peeped furtively over the rim of his perch at the rocks far below, but they offered no clue to his whereabouts in relation to the cove. All he could see was a jumble of weed-covered rocks against which the waves-appearing from his height as insignificant as ripples-beat with measured regularity. Above them, minute white specks, which he knew were gulls, soared aimlessly. For the rest, the ocean stretched, an infinite expanse of dark green water, to a hazy horizon.

The next matter that engaged his attention was the source of the water that filled the subterranean lake, for he saw at once that it could not enter the aperture through which he had reached the light of day, so returning a few paces into the cave he examined the roof closely. It was his ears rather than his eyes that provided the solution, for a steady trickle of water told him that tiny invisible streams were percolating through flaws in the rock and finding their way into the natural reservoir, which, at the time of heavy rain, must overflow with the results already noted.

As there was nothing more to see Ginger now gave serious thought to his position. He became aware that he was cold, which was not surprising since he was soaked to the skin-his second wetting within a few hours. He was worried, too, about his long absence from the base, which he knew could not fail to cause alarm, and might upset Biggles's plans. He had dismissed all idea of trying to get to the top of the rock, so it was obvious that the only way he could return to the depot was by the path he had come up, although this now presented difficulties that appalled him.

In the first place it meant a swim across the lake, with no a.s.surance that he would be able to find the fissure on the far side, or to climb up to it if he did find it. a.s.suming that he was successful so far, he was then faced With the disagreeable ordeal of dropping twelve feet in utter darkness on to a pile of boulders; for his matches, being wet, were now useless. He realized with an unpleasant twinge of fear that if he injured himself in the drop he was likely to die, in circ.u.mstances which he preferred not to contemplate. It is not surprising that the more he thought about things the less he liked the look of them, and sought desperately for an alternative.

Turning again towards the sea, it suddenly struck him that the watery sun might have sufficient power in it to dry his matches; if he could only get them dry, he thought, he ought to be able to transport them across the lake by tying them on his head. So with this object in view he took the box from his pocket and laid it, with the three matches beside it, in a sheltered pocket of rock reached by the sun. This done, he stood back prepared to await results. And he was still waiting, cold and uncomfortable, when a sound reached his ears that brought him round facing the sea, tense and expectant. It was the distant hum of an aero-engine ; and presently he saw the plane, which he recognized at once for one of their own, heading straight towards the rock. What was more, he perceived that if it held on its present course it would pa.s.s fairly close to him. If only he could attract the pilot's attention-for he did not know who was flying the machine, and was unaware of Algy's tragic discovery-it would alter the whole position. Those at the base would then guess what had happened, and presently come to his a.s.sistance. Even if they failed to find the fissure, he would, by signalling to them as they flew over, be able to ask for the things he most needed-food, a rope, and a new torch.

Watching the machine, with fading hopes he soon realized that the chances of his being seen were remote. The pilot might glance at the top of the rock in pa.s.sing, but he would hardly be likely to look closely at the face of the cliff, for there was no reason why he should. But if he, Ginger, could only reach the top, silhouetted against the skyline he could hardly escape being seen. Swiftly, he turned to make a closer inspection of the perilous pa.s.sage.

Now that he had become accustomed to the dizzy height it did not look so formidable, and almost before he had made up his mind seriously to attempt it he found himself on the bottom ledge, groping with his fingers for a firm hold. Finding one, he shifted his feet, and clawed again for a fresh cleft for his fingers. And so he went on, not once daring to look down, but keeping his eyes on the rim above as it drew imperceptibly nearer.

Gasping with fear and exertion, his clutching fingers at last closed over it, and with a haste made desperate by the now close proximity of the aircraft, he dragged his aching body over the top and rolled clear of the edge.

In a moment he was on his feet, waving frantically. He was just in time to see the machine glide out of sight round a shoulder of the rock.

Sick with disappointment, he sank down, and cupping his chin in his hands, gazed disconsolately at the empty sea.

CHAPTER XI.

WHAT HAPPENED TO BIGGLES.

WHEN he took off to look for Briny, the only doubt in Biggles's mind, apart from a natural concern about the lost sailor, was that, by force of circ.u.mstances, they were doing much more daylight flying than he had ever intended, more than Colonel Raymond had intended, and without question more than was safe if the secret of the base was to be guarded. His natural caution told him that they could not hope to go on flying daily over hostile waters, at all hours, without sooner or later being observed, and the suspicions of the enemy being aroused. Already their activities must have attracted attention, he reflected, as he pursued his allotted course, climbing all the time to obtain a wider field of view.

For the best part of an hour, like Algy, he was unsuccessful, seeing no craft of any sort ; and he was contemplating giving up the search when, far to the south, a minute object caught his eye. It was a vessel of some sort, but even at that distance he felt that it was too big to be the motor-boat. Nevertheless, he decided to make sure, so he flew on, and presently perceived that the object was not one boat, but two, a fairly large one with a smaller one moored close to it.

A suspicion was already forming in his mind as he throttled back and began a long glide, in this way losing height to get a clearer picture of what was happening ; and in a few minutes his suspicion was confirmed. The smaller of the two vessels was undoubtedly the missing motor-boat; the larger one, as far as he could make out, appeared to be a trawler or drifter. Considering the situation, he came to the natural conclusion that Briny had been found adrift by the larger boat, which had-as it was bound to-offered a.s.sistance, either by taking it in tow or supplying it with fuel.

The question that now automatically arose in Biggles's mind was the nationality of the drifter. If it turned out to be a German ship, then he could do nothing about it, for while he was prepared to take chances, it did not occur to him to attempt such a fantastic undertaking as to try to capture the ship single handed. What concerned him far more was the fact that by this time he was being watched by the crew, who would lose no time in reporting his position.

Instinctively his eyes went to the drifter's stern to see if she was flying her nationality flag; and he saw that she was. What was more important, it was not the flag of the German Mercantile Marine. He was unable to identify it ; all he knew was that it was not the German flag. And that was really all he cared about, for if it was not a German vessel it must belong to a neutral country, and since they were on the high seas he had nothing to fear.

Consequently, he continued the glide with the object of landing as close as he could to the two vessels, now lying hove to side by side. It may seem strange-and a few minutes later he was to reflect on this-that not for one single moment did it occur to him that the drifter might be flying false colours. So, with no suspicion in his mind, he made a good landing and without hesitation taxied up to the larger craft. It is true that it struck him as odd that Briny was not in sight, but he came to the natural conclusion that he was in the captain's cabin going through unavoidable formalities, in which case there was a chance that he might not have heard the approaching aircraft.

Still without the slightest suspicion of anything wrong, Biggles taxied right up to the drifter; and if he had entertained any doubts the behaviour of the crew would certainly have dispelled them, for they were leaning over the rail, smiling with what he took for amiability. So he made the Willie-Willie fast, and stepping out on to a float, climbed aboard.